In a gate restraining mechanism in a hydraulic turbine, the bolt must be prestressed so as to provide the necessary force to effect adequate clamping of the shear lever on a hub. In the past it has been the practice to provide an axial opening through the bolt and insert an electrical heater therein to elongate the bolt. After the bolt had been elongated, the end nuts were snugged up and the bolt was allowed to cool. This method is time consuming; and, also, by drilling the axial opening in the bolt to accommodate the electrical heater, the bolt was weakened. The electrical heating method was also hazardous to the personnel working around the hot parts.
It is the general purpose of this invention to provide a prestressing device which operates solely on the piece to be prestressed of a mechanical arrangement without reacting on any other component of the arrangement.
Another object of the present invention is to provide a prestressing device which is removable after prestressing has been accomplished.
The present invention includes a relatively long bolt which is provided for prestressing in lieu of the normal length clamp bolt. The threaded ends of the bolt receive the normal clamping nut, and the extreme ends of the bolt receive end nuts. Two levers are attached to the ends of the end nuts by means of removable pins. A hydraulic cylinder and piston mechanism is connected to act upon the other ends of the levers. A fulcrum bar connected between the ends of the levers acts as a fulcrum for the levers. As the hydraulic cylinder and piston pulls on the levers, the force is transmitted to the bolt which is elongated. The clamping nuts are snugged up and the pressure in the cylinder released. Thereafter the pins are removed releasing the device from the bolt and the attaching ends nuts removed.